1. Field of the Invention
This invention relates to a gas scavenger for educting gas away from semiconductor wafers as they are withdrawn from a processing chamber in a vertical or horizontal chemical vapor deposition furnace after being treated.
2. Description of the Related Art
In wafer fabrication processes such as diffusion, deposition, oxidation and annealing, semiconductor wafers in boats are treated in horizontal tubular chambers encircled with electrical heating elements with heated, toxic, flammable or corrosive gases. Gas scavengers are used at the exhaust ends of the tubes for educting these gases into the house exhaust systems. FIG. 1 is a plan sectional view of a typical hot wall process tube 24 in a furnace 23 and a scavenger 30 fastened to its exhaust end 26. Gas flows into the source end 25 of the process tube 24, out through the exhaust end 26 into the scavenger 30 and then into an exhaust port 32 connected to the house exhaust system 33. Also, air flows into the scavenger 30 through its usually uncovered outboard end 34 and then through the port 32 into the house exhaust system 33. Such scavengers are typically about twelve to fifteen inches square and about twelve to eighteen inches deep.
After processing and while the process or purge gas is flowing, the wafer-ladened boats 22 are withdrawn by boat loaders (not shown) from the process tube 24 through its exhaust end 26 into the scavenger 30 and then to a loading/unloading station in the air (not shown). As FIG. 1 illustrates, the design of such scavengers causes turbulent gas currents 28 in the scavenger to flow through the wafers 20 as a boat 22 is withdrawn from the process tube 24. This causes particulates trapped in the scavenger 30 to become entrained in the gas along with the entrained particles from the process tube 24 and to deposit on the surfaces of the wafers 20 as the gas flows through the boat. In addition, air currents 36 are drawn across the boat 22 path of travel as well.